From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2C4972882A7; Thu, 15 May 2025 08:22:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747297379; cv=none; b=SVTycP7A9pcZyANcp0ob0c3o7R3oeuNQ5JUrQJ+j0wGNIKiGCGk4TMdItiLkS5eD81AugLi+LiZfOkVXKLVXkGJrYrUxfNT/U2jxF9KzaJlakg7tUL4fY3M04bDetwimiOyME/9/rJ09c/8H11kmDXo2niK8TYZIhkdKcPbDrHE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747297379; c=relaxed/simple; bh=//mSUgnmlOwn4ta+iofpVHMNtGUvxgT5BbmIcrDJCAE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZZ+bUIc7UC7uo6cX7eREqWPO2zyihbDoldAbHCwntaF6ydKEIurh/LKk+D2IzIPkLP/anKcwf/4GiyLA4FpOBQjXtOj7cjtX75IStoV2poBT1jJ2CpYRlm/aQ6K2+xMlfXiJAm72jG5XGNNOBQwQw/RfI7odOjJ52+YzwAQZ3LU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B5D5C14BF; Thu, 15 May 2025 01:22:44 -0700 (PDT) Received: from [10.162.40.26] (K4MQJ0H1H2.blr.arm.com [10.162.40.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8CD1A3F673; Thu, 15 May 2025 01:22:53 -0700 (PDT) Message-ID: <4904d02f-6595-4230-a321-23327596e085@arm.com> Date: Thu, 15 May 2025 13:52:50 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: Check pxd_leaf() instead of !pxd_table() while tearing down page tables To: David Hildenbrand , catalin.marinas@arm.com, will@kernel.org Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, mark.rutland@arm.com, yang@os.amperecomputing.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org References: <20250515063450.86629-1-dev.jain@arm.com> <332ecda7-14c4-4dc3-aeff-26801b74ca04@redhat.com> Content-Language: en-US From: Dev Jain In-Reply-To: <332ecda7-14c4-4dc3-aeff-26801b74ca04@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15/05/25 1:43 pm, David Hildenbrand wrote: > On 15.05.25 08:34, Dev Jain wrote: >> Commit 9c006972c3fe removes the pxd_present() checks because the caller >> checks pxd_present(). But, in case of vmap_try_huge_pud(), the caller >> only >> checks pud_present(); pud_free_pmd_page() recurses on each pmd through >> pmd_free_pte_page(), wherein the pmd may be none. > The commit states: "The core code already has a check for pXd_none()", > so I assume that assumption was not true in all cases? > > Should that one problematic caller then check for pmd_none() instead? From what I could gather of Will's commit message, my interpretation is that the concerned callers are vmap_try_huge_pud and vmap_try_huge_pmd. These individually check for pxd_present(): if (pmd_present(*pmd) && !pmd_free_pte_page(pmd, addr)) return 0; The problem is that vmap_try_huge_pud will also iterate on pte entries. So if the pud is present, then pud_free_pmd_page -> pmd_free_pte_page may encounter a none pmd and trigger a WARN. > > If you were able to trigger this WARN, it's always a good idea to > include the splat in the commit. I wasn't able to, it is just an observation from code inspection. >